1. Field of the Invention
This invention relates to automatic door operators and, more particularly, to door operators having obstruction detectors.
2. Description of the Prior Art
There have been various types of obstruction detectors for use in garage door operators. The oldest system consisted of a torque sensor in the motor of the door operator itself. If the sensor detected excess torque, such as caused by the door attempting to close upon something that was in its path, the door stopped and reversed.
There has recently been increased attention paid to garage door operator safety. Federal legislation has been passed, as well as legislation in several states, including Minnesota and California. The purpose of this legislation is to provide additional safety features to residential garage door operators beyond the traditional torque sensors. The California law requires the inclusion of a tactile garage door edge sensor, an optical sensor or similar device that, when activated, is designed to cause a closing door to open and prevent an open door from closing.
Edge sensors and optical or light beam sensors are two of the more popular obstruction detectors currently being used. Edge sensors are commonly used in elevator doors and also are designed specifically for use on the bottom edge of garage doors. An edge sensor device typically comprises a strip placed along the leading edge of the door providing a multiplicity of parallel open switches spaced along the door edge. When pressure is applied to any spot on the strip, one or more of the switches closes, producing a closed-circuit. Edge sensors thus provide an open-circuit when no obstruction is sensed and provide a closed-circuit when an obstruction contacts the sensor.
Light beam sensors recently have become popular. These systems typically include an infrared light emitter positioned on one side of the garage doorway and an infrared sensor on the other side. The emitter produces a light beam that is aligned so that it extends across the doorway and strikes the sensor on the other side. As long as the sensor detects the light beam, the sensor outputs a low-level signal. When the light beam is broken and the sensor does not detect the presence of the light beam, the sensor outputs a high-level signal indicating the presence of an obstruction in the doorway.
These obstruction detectors can be connected to the door operator by three lines, a supply line, a signal line and a ground line. The supply line typically supplies 20 to 30 volts from the power supply of the door operator to the remote obstruction detector. The signal line provides a signal from the obstruction detector to the door operator. The ground line supplies a reference signal from the door operator to the remote detection device. The voltage on the signal line is close to the supply voltage when the obstruction sensing device senses an obstruction and is close to ground when no obstruction is sensed.
As long as the door operator receives a low-level output signal from the obstruction detector on the signal line, the operator operates normally, opening and closing the door. When a high-level output signal is received from the obstruction detector, the signal is an indication that an obstruction has been detected, and the door operator stops the door if it is closing and reverses it. (If the door is already going up when an obstruction is detected, the operator continues opening the door.) As long as an obstruction continues to be sensed, the operator will not permit the door to close.
These existing obstruction detectors are generally very effective in sensing an obstruction and the door operator takes the appropriate action in response. However, the obstruction detectors are only effective as long as they work and as long as the wiring from the door operator to the detector is operating properly.
While the wiring within the door operator/control circuit is usually well protected (and correctly wired), obstruction detection usually requires that the obstruction detector be located near the floor or the bottom of the door, remote from the detector. This exposes the detector wiring to physical hazards and potential wiring errors. If one of the wires from the obstruction detector to the door operator breaks or is damaged or if the wires short out, the signal from the obstruction detector will be unreliable. If certain wires short or open, the system will produce a high-level signal which will cause the door operator to keep the door open. However, if certain other conditions occur, it is possible for the door operator to continue to receive a low-level signal from the obstruction detector even though there is an obstruction in the doorway.
For example, if the supply line and the signal line short together, a high-level signal will be present on the signal line regardless of the presence of an obstruction. If the signal line and the ground line short together, a low-level signal will always be present on the signal line regardless of the presence of an obstruction. If the supply line or the signal line is damaged creating an opening-circuit on either line, a low-level signal will always be present on the signal line regardless of the presence of an obstruction. Similarly, if the ground line is damaged creating an open-circuit on that line, a high-level signal will always be present on the signal line regardless of the presence of an obstruction.
Also, if the obstruction detector itself malfunctions, a continuous high-level or low-level signal may be present on the signal line regardless of the presence of an obstruction. While a false indication of an obstruction would merely result in the operator refusing to close the door, a false indication of the absence of an obstruction could result in the operator allowing the door to erroneously close.